In an analysis of mammalian oogenesis, one cannot investigate the oocyte without studying the companion multifunctional granulosa cell and associated structures, i.e. basement membrane, vascularized theca interna, and the non-vascularized theca externa. Thus, in a sense, mammalian oogenesis becomes a study of the ontogeny of the highly, hormonally integrated, Graafian follicle. The objective of this research proposal is to learn some of the basic, fundamental aspects of the dynamic morphology of mammalian oogenesis and folliculogenesis. Special attention will be given to the onset or initiation and maintenance of meiosis I, surface characteristics of the plasma membrane of the granulosa cell that accompany its differentiation by use of plant lectins, and a selective permeability of the basement membrane as it relates to the maintenance of the unique microenvironment of the developing Graafian follicle, under both normal and experimental conditions. The proposed experiments will utilize in vivo and in vitro techniques (tissue and organ culture), electron probe microanalysis, freeze fracture, transmission and scanning electron microscopy, fluoresceine and ferritin conjugated lectins as membrane probes, radioimmunoassay, and cytological procedures.